ral-bearing limestones of the Middle Devonian of Devonshire
and the great "Eifel Limestone" of Germany.

(3) The _Hamilton Group_--consisting of shales at the base
("Marcellus shales"); flags, shales, and impure limestones ("Hamilton
beds") in the middle; and again a series of shales ("Genesee
Slates") at the top. The thickness of this group varies from
200 to 1200 feet, and it is richly charged with marine fossils.

(4) The _Portage Group_.--A great series of shales, flags, and
shaly sandstones, with few fossils.

(5) The _Chemung Group_.--Another great series of sandstones and
shales, but with many fossils. The Portage and Chemung groups
may be regarded as corresponding with the Upper Devonian of
Devonshire. The Chemung beds are succeeded by a great series
of red sandstones and shales--the "Catskill Group"--which pass
conformably upwards into the Carboniferous, and which may perhaps
be regarded as the equivalent of the great sandstones of the
Upper Old Red in Scotland.

Throughout the entire series of Devonian deposits in North America
no unconformability or physical break of any kind has hitherto been
detected; nor is there any marked interruption to the current of
life, though each subdivision of the series has its own fossils.
No completely natural line can thus be indicated, dividing the
Devonian in this region from the Silurian on the one hand, and
the Carboniferous on the other hand. At the same time, there is
the most ample evidence, both stratigraphical and palaeontological,
as to the complete independence of the American Devonian series
as a distinct life-system between the older Silurian and the
later Carboniferous. The subjoined section (fig. 76) shows
diagrammatically the general succession of the Devonian rocks
of North America.

[Illustration: Fig. 76. GENERALIZED SECTION OF THE DEVONIAN ROCKS
OF NORTH AMERICA.]

[Illustration: Fig. 77.--Restoration of _Psilophyton princeps_.
Devonian, Canada. (After Dawson.)]

As regards the _life_ of the Devonian period, we are now acquainted
with a large and abundant terrestrial _flora_--this being the
first time that we have met with a land vegetation capable of
reconstruction in any fulness. By the researches of Goeppert,
Unger, Dawson, Carruthers, and other botanists, a knowledge has
been acquired of a large number of Devonian plants, only a few
of which can be noticed here. As might have been anticipated,
the greater number of the vegetable remains of t